A hallucination is something that someone experiences which is not really there.

Probably the best way to describe a hallucination is that it is like dreaming while you are awake. Not daydreaming, which comes from conscious thoughts, but the things contained in your sub-conscious which are projected from your mind and appear to blend in with the real world. Hallucinations can be quite deceiving (especially if it is a mix of a visual images, sound and even the sensation of touch) and, like dreams, sometimes you know it’s not real but other times you are unsure. Also like dreams, hallucinating can warp or distort your thinking, causing you to know things you shouldn’t and to completely forget things that are common sense, obvious and every day practice.

There are five different types of hallucination:
* visual (seeing things)
* auditory (hearing things)
* olfactory (smelling things)
* gustatory (tasting things)
* tactile (feeling things)
Often, two or more of these will be mixed together at the same time.

Hallucinating can happen to anyone at all, and at any age. Some people hallucinate on a daily basis, while others may only experience it once and even then very briefly in their entire life.
Taking certain drugs may result in hallucinating, while for others, they may hallucinate because they have a mental illness or even for no obvious reason at all (even though there probably is a reason). For those who don't use drugs to hallucinate, different things can trigger it such as being alone, being around too many people, too much noise, no noise, the dark, etc.

The ceiling began to ripple like water and I could hear screaming, but it was just a hallucination.